1. Field of the Invention
The present invention relates to an exposure apparatus and a method of manufacturing an article.
2. Description of the Related Art
One of apparatuses used in a manufacturing step (lithography step) for a semiconductor device or the like is an exposure apparatus which transfers the pattern of a mask onto a substrate coated with a resist. Recent micropatterning of semiconductor devices and the like requests the exposure apparatus to accurately transfer, onto a substrate, a pattern formed on a mask. For this purpose, it is important to make the imaging plane (focus plane) of the projection optical system coincide with the substrate surface. The exposure apparatus therefore performs focus measurement to measure the height of the substrate surface.
In the exposure apparatus, focus measurement is generally performed while moving a substrate at a constant velocity. However, to increase the productivity (throughput), the exposure apparatus needs to perform focus measurement even in a state in which the acceleration of a substrate stage holding a substrate is nonzero, that is, a state in which the substrate stage is accelerated or decelerated. Japanese Patent Laid-Open No. 2011-238707 discloses a method of performing focus measurement in a state in which the substrate stage is accelerated or decelerated, and correcting the result based on a correction value obtained in advance.
Generally in the exposure apparatus, a plurality of timings to perform focus measurement are set at equal intervals. However, when an exposure apparatus configured to perform focus measurement at a plurality of timings set at equal intervals performs focus measurement in the state in which the substrate stage is accelerated or decelerated, a plurality of measurement portions on a substrate to undergo focus measurement are not equally spaced.